Dimensions of Envelope Sizes: Your Complete UK Envelope Guide

Dimensions of Envelope Sizes: Your Complete UK Envelope Guide

Choosing the right envelope size is essential for professional, well-presented mail. Whether you’re sending letters, invitations, or printed marketing materials, knowing the correct envelope dimensions ensures your contents fit perfectly and arrive in great condition. In this guide, we’ll explore the most common envelopes, from C4 and C5 envelope sizes to DL and C6 envelope measurements.

Envelope Size Measurements Quick Reference

Use this quick reference when designing or printing custom envelopes to make sure your artwork and contents align with standard envelope dimensions.

Understanding Envelope Dimensions

Envelope sizes in the UK are typically based on ISO paper standards, which are according to Wikipedia, the standard "A", "B" and "C" series of paper sizes. (Wikipedia) For example, a C4 envelope size fits an A4 sheet without folding, while a C5 envelope size fits an A5 sheet or an A4 folded once.

C series sizes are used to prevent damage and make it easier for the user to send their documents off. If you were to use A series sizes, letters may struggle to fit inside the envelopes, leading to damage and scrunching to fit them inside.

Here’s a quick breakdown of how some common envelope dimensions work and what they are used for:

    •    C-series envelopes correspond to A-series paper sizes, C5 for A5, C4 for A4, ect.

    •    C6 envelopes are often used for cards and personal notes.

    •    C5 and C4 envelopes are commonly used for letters and documents.

    •    DL envelopes are longer and narrower, perfect for tri-folded A4 letters and used commonly for official letters.

    •    Measurements are given in millimetres (mm) for precision and postal compatibility.

For a deeper explanation on paper sizes and the ISO standard, discover our article here.

Standard UK Envelope Sizes and Dimensions

These are the standard envelope sizes UK printers and stationary suppliers use. When ordering, always double-check envelope measurements to ensure your print fits neatly.

Most Common Envelope Sizes

Some of the most commonly used envelopes in the UK include the C4, C5, C6 and DL sizes — each designed for specific document formats and uses.

C4 Envelope Measurements

The C4 envelope measures 229 x 324 mm 22.9 x 32.4 mm 9 x 12.8 inches A4 envelopes are perfect for sending important documents, certificates, brochures, or reports flat without folding, ensuring a neat and professional presentation. These fit A4 sheets flat and are commonly used for official documents, reports, and catalogues. These are not as common as DL or C5.

C5 Envelope Measurements

The C5 envelope measures: 162 × 229 mm 16.2 x 22.9 cm 6.3 x 9 inches It’s a popular choice for letters, marketing materials, and event invitations, offering a compact yet professional look. These envelope sizes are perfect for A5 sheets or A4 paper folded once. You can fold down large pieces of paper further, but you risk damaging the document inside due to over-folding.

C6 Envelope Measurements

The C6 envelope measures: 162 × 114 mm 16.2 x 11.4 cm 4.5 x 6.4 inches C6 envelopes are perfect for sending greeting cards, thank-you notes, RSVP replies, and small invitations, offering a compact and elegant presentation. Ideal for A6 cards or A5 sheets folded once or for a quality card and envelope

DL Envelope Measurements

The DL envelope measures: 110 x 220 mm 11 x 22 cm 4.3 x 8.7 inches Designed to fit an A4 sheet folded into thirds, perfect for business letters, invoices, and marketing correspondence. Here are the sizes all lined up together.

Professional Custom Envelope Printing

At GD Print, with our 40+ years of printing experience, we supply and print high-quality envelopes in all standard sizes, including C4, C5, C6, and DL. You can customise your envelope design online, adding your logo, return address, or full-colour branding for a polished, professional appearance.

We offer premium 120gsm envelopes with strong adhesive seals — ideal for marketing, mailers, or corporate stationery. With fast UK delivery, you’ll get perfectly printed envelopes every time. 

Discover our custom envelopes here.

Summary

Understanding the dimensions of envelope sizes helps ensure your prints look their best, fit correctly, and post easily. From A4 envelope dimensions to C5 envelope measurements, GD Print provides every size you need for professional presentation — with reliable printing, quality materials, and quick turnaround.